Method and device for making aluminum electrodes



P 1941. A. F. P. J. CLAASSEN ET AL 2,255,860

METHOD AND DEVICE FOR MAKING ALUMINUM ELECTRODES Filed April 26, 1939 Patented Sept. 23, 1941 OFFICE.

METHOD DEVICE FOR MAKING ALUMINUMELECTRODES Anthony Frederik Peter Johannes Claassen and Johan Dirk de Vries, nmonoven, Netherlands,

assignors, vby mesne assignments, to Hartford National Bank and Trust Conm, as trustee Company, Hartford,

Applicatiii: April 26, 19 sensiisa zvazec Germany Mayiii. 1938 Our invention relates to a method and device for-increasing the active surface area of aluminum electrodes, particularly electrodes for electrolytic condensers, by chemical agency.

The term chemical agency is tube understood to include the usual chemical cauteriz'ation or etching, as well as cauterization or etching by electrochemical agency.

To increase the active surface area of aluminum electrodes it is known to cauterize them, for example in hydrochloric acid, and in such cases the temperature of the cauter bath employed was usually about 20 to 0., but higher temperatures have been suggested. In view of the generally recognized fact that the rapidity of areaction is materially increased with an increase of temperature, one skilled in the art had come to the conclusion that the temperatureof the r usually employed. 1 I Furthermorawe have found that such a material increase is not obtained by coolingrthe solution with comparatlvely cold tap water. 4

, .We-have found thatthe improved results obtainedby the present invention are due solely to increase in theactive surface is obtain d only cauter bath should be as high as possible to in- I sure a sufliciently quick cauterizing effect. For example, the British Patent 448,163 suggests that the temperature of the cauter solution be maintained at'the boiling point, i. e. at approximately 100 C.

We have found that when the cauter solution is maintained at such relatively high temper-' atures, it is impossible to obtain with uniformity a material increase in the active surface area. More particularly, although the usual methods of cauterization make it possible to obtain with regular results an electrode which gives a capacity of from four to eighttimes that obtained diflicult, if not impossible, to obtain with such methods a greater surface increase in mass production.

The main object of our invention is to produce a greater increase in the active surface area of an aluminum electrode by chemical agency.

A further object is to provide a method of increasing the active surface area with which uniform results can be obtained in mass production.

Further objects'of our invention will appear as the description progresses.

if the. temperature of the 'solution' is mai tained within the above-mentioned range.

' In orderthat the invention may be more clear-' 1 understood and readily carried into effect, we shall describe the same in more detail with reference to .the accompanying drawing, in which,

. Figure 1 is a sectionized side view of an apparatus in which the cauter liquid is indirectly o ed. nd

Fig. 2 is a sectionized view of an apparatus in which the cautersolution is directly cooled.

The apparatus shown in Figure '1 comprises a suitable container I filled with a cauter solution I, for example a solution consisting of hydro-v ,chloric acid and a small addition of aluminum with an electrode having smooth surfaces, it is chloride. Container I0 is partly immersed within a cooling liquid 3, such as a solution of salt tion indicated by the arrows. In the present instance the cauter solution is maintained at a tenfperature between 2 C. and 8 C. and preferably at a temperature of about 5-6 C.

In Figure 2 a container l I is filled with a cauter solution I, also containing a solution of hydrochloric acid. The solution I is maintained at a 5 temperature below 8 C. and above its freezing According to the invention, we maintain the tion is maintained at the higher temperatures point, for instance at a temperature of about 6 C., by a cooling coil 6 through which a suitable refrigerant, such as glycerine dissolved in water, supplied from a refrigerator 8 is circulated by a The method according to the invention may be used independently or in conjunction with known niethods for obtaining a highly enlarged whose copper percentage is kept below a certain value, for instance 0.05%, to improve the cauter-c izing effect; also for types of aluminum having a very small crystal-grain size, for instance 1 micron;

The advantage of the method according to the invention over prior-art methods will clearly appear from the following comparison test.

Electrodes having a geometric or contour surface area of about 100 sq. cm. were made from aluminum having a purity of aboiit 99.85%. The cauter bath used consisted of a solution of approximately 9% hydrochloric acid in distilled water, to which was added a quantity of aluminum chloride (AlCla) corresponding to a quantity of 20 grams of aluminum per liter. According to tests, this proved to be a concentration yielding the largest surface increase. The temperature of the center bath was maintained at about 20 C. and the electrodes were cauterized for 1 /2 hours in this solution and then formed to a voltage of 500 volts. We found that the electrodes had a capacity of from 8 to 9 microfarads, and these results could be uniformly produced in mass production. With a longer duration of cauterizing the capacity did not increase further.

g In accordance with the invention, the above tests were repeated under the same conditions except that the cauter bath was maintained at a temperature of about 6 C. and the duration of cauterizing was increased to 343 hours. For

electrodes having the same contour surface area and with the same formation process a capacity of 14 to 15 pf was now obtained.

Even when the surface enlargements obtained will slightly vary through various influences, itis yet possible to obtain in a reproducible manner an improvement of the active factor of surface increase which materially exceeds 50% with regard to the factors obtained heretofore.

It should be noted that because of the reduction in the geometric dimensions of the electrodes, the method according to the inventionresults in an increase of the series resistance in because obvious modifications will occur to a per-- son skilled in the art.

Whatwe claim is: 1. A method of increasing the active surface of an aluminum electrode by chemical agency,

comprising the steps of placing the electrode in an etching solution, and maintaining the solution at a temperature above its freezing temperature and below 8 C.

2. In the treatment of aluminum electrodes with'an etching solution to increase the surface area by chemical agency, cooling the solution to a temperature above its freezing temperature and below 8 C. i

3. A method of increasing the active surface of an aluminum electrode by chemical agency, comprising the steps of placing the electrode in an etching solution containing hydrochloric acid, and maintaining the solution at a temperature above its freezing temperature and below about 8 C.

4. A method of increasing the active surface of an aluminum electrode by chemical agency, comprising the steps of placing the electrode in an etching solution of hydrochloric acid and aluminum chloride, and maintaining the solution at a temperature above its freezing temperature and below about 8 C.

5. A method of increasing the active surface 'of an aluminum electrode by chemical agency comp ing the steps of placing the electrode in a 9% ydrochloric acid aqueous etching solution, and maintaining the etching solution at a temperature above its freezing temperature and below about 8 C.-

JOHAN DIRK DE VRIES. 

